The present invention relates to a motor driven power steering (MDPS) and a method for driving the same, and more particularly, to an MDPS and a method for driving the same, which estimates the temperature of a motor by reflecting the thermal characteristic (heat radiation performance) of the MDPS depending on a traveling state of a vehicle, and controls an amount of current applied to the motor.
Since MDPS generates an assist thrust through a motor, each upper logic calculates a proper command. The command is closely related to column torque measured by MDPS in terms of performance, but closely related to protection logic such as over heating protection (OHP) logic in terms of fail-safe logic.
That is, when MDPS operating logic illustrated in FIG. 1 senses a motion of a steering wheel by a driver, a command calculated through steering performance logic is passed through torque limit logic to limit excessive torque, and steering torque is generated by a command calculated through motor control logic.
The torque limit logic is protection logic which limits a motor output to safely operate MDPS, when MDPS is not in a normal state.
Representative examples of the torque limit logic may include OHP logic. When a power pack (ECU+motor of MDPS) is overheated, the OHP logic reduces torque commands and uses a minimum amount of current to prevent the power pack hardware from being overheated and burned out.
In many cases, the OHP logic is operated through only one temperature sensor, in order to reduce cost. Using a value calculated from a temperature estimation function for the position of each part (motor, ECU, or temperature sensor) based on a temperature sensor mounted in the ECU, the OHP logic of the fail-safe logic may limit the maximum current when an estimated temperature for each part reaches a critical temperature, or may reduce the magnitude of the maximum current according to the estimated temperature.
However, since such a method estimates the temperature using one temperature sensor, the temperature for each part cannot be precisely estimated. In particular, each part within the power pack, such as FET, motor, or power module, has a different temperature increase characteristic. Thus, the performance of the part may be degraded by overheat due to a difference between the estimated temperature and the measured temperature, or the performance of the system may be degraded by excessive application of the fail-safe logic.
The related art of the present invention is disclosed in Korean Patent Laid-open Publication No. 10-2012-0019889 published on Mar. 7, 2012 and entitled “System and method for over heat protection of motor for motor driven power steering”.